Liver cell proliferation after partial hepatectomy in rats has been thoroughly investigated. Althorough DNA synthesis and morphological restoration has been studied in this rat model, functional capacity of the remnant liver during regeneration after hepatectomy has not been elucidated.We measured the ICG diaappearance rate (ICG-k) and serum aminopyrine and antipyrine clearance (CLamp, CLant) in rats at various intervals after 70% hepatectomy. ICG was measured with a photosensor (RK-1000) . Serum aminopyrine and antipyrine were measred by gas liqid chromatography. Morphological restoration of the liver after hepatectomy was evaluated based on remnant liver weight, the PCNA labeling index, and the DNA content of the regenerating liver. Serial changes in ICG-k, CLamp, and CLant after hepatectomy were compaired with the morhological restoration.ICG-k and CLamp were reduced by about one-third in 70% partial hepatectomy. Although restoration of remnantliver weight occurred steadily after the operation, ICG-k, CLamp, and CLant were lowest adout 36 hours after the operation. ICG-k was comparatively restored along with liver weight. The restoration of CLamp and Clant was delayd.Functional liver mass was minimal during parenchymal cell mitosis in the regenarating liver. Functional restoration after hepatectomy was delayd in comparison with morphological restoration.